Apparatus and method for electrochemical processing of thin films on resistive substrates

ABSTRACT

An electrochemical process comprising: providing a 125 mm or larger semiconductor wafer in electrical contact with a conducting surface, wherein at least a portion of the semiconductor wafer is in contact with an electrolytic solution, said semiconductor wafer functioning as a first electrode; providing a second electrode in the electrolytic solution, the first and second electrode connected to opposite ends of an electric power source; and irradiating a surface of the semiconductor wafer with a light source as an electric current is applied across the first and the second electrodes. The invention is also directed to an apparatus including a light source and electrochemical components to conduct the electrochemical process.

This application is a Divisional of co-pending application Ser. No.12/198,274, filed on Aug. 26, 2008, which is a Continuation ofco-pending application Ser. No. 11/417,146, filed on May 4, 2006, andfor which priority is claimed under 35 U.S.C. §120. The entire contentsof each application is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the electrochemical processing of thin filmsdirectly on semiconducting or insulating layers and an apparatus forimplementing such processes.

BACKGROUND OF THE INVENTION

In semiconductor manufacturing and, in particular, for forming metallayers or interconnects, the metal is typically electrodeposited on ametallic seed or plating base layer. The seed layer is typically formedon a semiconductor wafer by physical vapor deposition (PVD) or chemicalvapor deposition (CVD). The current flow driving the electrodepositionis passed laterally through the seed layer from the electrical contactestablished at the seed layer edges. Current through the semiconductorwafer itself and any dielectric layers contained within thesemiconductor wafer is essentially negligible.

Electrochemical processing of semiconducting/insulating materials canoccur where the semiconductor wafer, typically a thin oxide coating orsemiconductor, can conduct small amounts of an electric current.Conductance can be provided by transport of charges directly through thevalence or conduction band of a semiconducting/insulating semiconductorwafer. The latter case becomes important when working withsemiconducting oxides such as TiO₂, ZnO and Ta₂O₅, as well as any n-typewide band-gap semiconductor. For thin oxide/insulating layers, electrontunneling or current leakage can also be a mechanism for conductivity.Defects can also provide many electron states in the band gap of aninsulator and for a high density of gap states these defects can providea pathway for the electric current.

This principle is illustrated schematically in FIG. 1. When emptyoxidant states in solution overlap with the electron states of aconduction band of a semiconductor (FIG. 1A), electroreduction ofoxidants will be possible at an n-doped semiconductor wafer (conductionband electrons available) but not at a p-doped semiconductor wafer (noconduction band electrons available in the dark). If the Gaussiandistribution of oxidant states corresponds with energies in the band gapof a semiconductor, no charge transport will be possible and the oxidantcan be expected to be inactive at this particular semiconductor wafer(FIG. 1B). However, if oxidant states in solution overlap with thevalence band of a semiconductor, charge transfer is possible both forn-doped as well as p-doped semiconductor wafers (FIG. 1C). In sum, theelectronic structure of the insulator and semiconductor semiconductorwafer in combination with the electronic structure of the redoxelectrolyte in solution allows for only certain charge transfercombinations.

SUMMARY OF THE INVENTION

An electrochemical method comprising: providing a 125 mm or largersemiconductor wafer in electrical contact with a conducting surface,wherein at least a portion of the semiconductor wafer is in contact withan electrolytic solution, and the semiconductor wafer functions as afirst electrode; providing a second electrode in the electrolyticsolution, wherein the first and second electrodes are connected toopposite ends of an electric power source; and irradiating a surface ofthe semiconductor wafer with a light source as an electric current isapplied across the first and the second electrodes.

In one embodiment, the electrochemical method is a cathodicelectrodeposition process of a 125 mm or larger, p-type semiconductorwafer with an optional insulating layer. The process comprises:positioning the p-type semiconductor wafer in an electrolytic solution;positioning a counter electrode in the electrolytic solution;illuminating a front side of the p-type semiconductor wafer or theinsulating layer, if present, or illuminating a back side of thesemiconductor wafer, with a light source; and applying an electriccurrent to the semiconductor wafer and to the counter electrode.

In another embodiment, the electrochemical method is as an anodicelectrochemical process of a 125 mm or larger, n-type semiconductorwafer with a metal layer. The anodic process comprises: positioning thep-type semiconductor wafer in an electrolytic solution; positioning acounter electrode in the electrolytic solution; illuminating a frontside or the back side of the n-type semiconductor wafer with a lightsource; and applying an electric current to the semiconductor wafer andto the counter electrode. Typically, the anodic electrochemical processis an electroetching process of the metal layer or an anodizationprocess of the metal layer.

The invention is also directed to an apparatus including a light sourceand electrochemical components to conduct the electrochemical methods ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become apparentupon consideration of the following detailed description of theinvention when read in conjunction with the drawings, in which:

FIGS. 1A to 1C show schematic illustrations of electronic configurationsfor conduction and valence bands in a semiconductor wafer and an oxidantcontaining solution, with a Gaussian distribution of density of electronstates;

FIGS. 2A and 2B show, in cross sectional view, a schematic illustrationof blanket electrodeposition using through-gate dielectric current flow;

FIG. 3 shows current-voltage curves for n-type and p-type Si/SiO₂(1nm)/HfO₂(3 nm) in a nickel sulfate solution in the dark and underwhite-light illumination;

FIGS. 4A and 4B show, in cross sectional view, a schematic illustrationof the selective photo-electrodeposition of a metal pattern on a blanketgate dielectric by illumination of the semiconductor wafer through amask while applying a potential or current;

FIG. 5 is a schematic representation of an apparatus of the invention;

FIG. 6 is a schematic representation of another apparatus of theinvention;

FIG. 7 is a schematic representation of another apparatus of theinvention;

FIG. 8 is a schematic representation of another apparatus of theinvention;

FIG. 9 is a schematic representation of another apparatus of theinvention;

FIG. 10 shows a 200 mm silicon wafer electroplated selectively withcopper;

FIG. 11 is a graphical representation of capacitance-voltagecharacteristics for Re gates measured with a 100 μm×100 μm MOS teststructure;

FIG. 12 exhibits the XRD diffraction patterns for deposited rutheniumusing conventional methods known in the art and using thephoto-electrodeposition process of the invention; and

FIG. 13 exhibits the XRD diffraction patterns for deposited rheniumusing conventional methods known in the art and using thephoto-electrodeposition process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The generation of an electrochemical current at thesubstrate/electrolyte interface in an electrochemical reaction dependson several factors. In the case of a metal semiconductor wafer, suchstudies are focused on the electrolyte interaction since the electronsrequired for the reaction are available in abundance at all possibleenergy levels. However, in the case of a semiconducting or insulatingsemiconductor wafers, attention should be directed to semiconductorwafer/electrolyte interactions. These factors include: the energeticposition and density of electron states of the electrolyte with respectto the valence band edge as well as the conduction band edge of theoxide and underlying semiconductor wafer. Conductance is dependent onwhether charge transfer at an interface occurs between filled and emptyelectron states.

The present invention describes an electrochemical process for obtainingthin films directly on a 125 mm or larger semiconductor wafer with orwithout an insulating layer, and an apparatus to conduct the process.The electrochemical process comprises a backside contact scheme forelectrical connection to a semiconductor wafer with or without aninsulating layer, wherein the top surface of the semiconductorwafer/layer acts as an electrode, e.g., a working electrode, in theelectrochemical process. The desired electrochemical reaction can occuron the surface of the semiconductor wafer. Alternatively, the desiredelectrochemical reaction can occur on a thinmetallic/semiconductor/insulating layer disposed on top of thesemiconductor wafer. The process does not require an underlying seedlayer to carry the current.

FIGS. 2A and 2B illustrate a contact scheme of one embodiment of theinvention. A dielectric layer 2 (also referred to as an insulating layeror insulator) such as a thin gate oxide is placed atop a 125 mm orlarger semiconductor wafer 4 such as silicon. Electrical contact 5 ismade to the semiconductor wafer 4 as a backside contact. Alternatively,if the insulating layer 2 is a semiconductor (such as a wide band-gapsemiconductor, for example, n-ZnO, n-TiO₂ or n-Ta₂O₅) for which an ohmiccontact scheme is known, an electrical contact can be made directly tothe insulating layer. An electrolyte solution 1 is placed in contactwith dielectric layer with the semiconductor wafer front side fullysubmerged, or optionally, with the semiconductor wafer partiallysubmerged in areas where processing is desired. The semiconductor waferacts as one electrode and a counter electrode 6 is positioned in theelectrolyte solution. While semiconductor wafer 4 and insulating layer 2of FIG. 2 are shown as planar, it is understood that semiconductor wafer4 can also have some topography and insulating layer 2 can be aconformal layer.

For electrochemical processing an electrical current is applied to thesemiconductor wafer (electrode) 4 and the counter electrode 6 via apower supply 7 and electrical leads 8. If desired, the electrochemicalpotential of the structure/electrolyte can be controlled more accuratelyby the introduction of a third electrode, that is, a reference electrode(not shown), which has constant electrochemical potential. Examples ofreference electrodes include a saturated calomel electrode (SCE) andsilver-silver chloride (Ag/AgCl) reference electrodes or other metalreference electrodes such as Cu or Pt. FIG. 2B shows the formation of aplated metal film 9 at the structure/electrolyte on the dielectric orinsulating layer 2. Although the scheme of FIG. 2 depicts the plating ofa metal film 9, one of ordinary skill in the art would recognize thatvariations of the scheme of FIG. 2 would include other electrochemicalprocesses such as etching or anodization of metals to selectivelygenerate thin layers of interest.

Due to the strongly resistive nature of the electron transfer processacross a 125 mm or larger semiconductor wafer with or without aninsulating layer, electrochemical processing can be expected to occurpreferentially on regions that are the most conductive since the currentwill follow the path of least resistance. In this regard,electrochemical processing by current transport across suchsemiconductor wafers can be an extremely selective process. Severalfactors or parameters may determine the selectivity and include:underlying semiconductor wafer, insulator thickness, type of insulator,electrolyte solution, physical blockage, light, and other externalmeans.

Current-voltage characteristics, and thus electrode kinetics, are alsodetermined by the makeup of the underlying semiconductor wafer. Thesecharacteristics may vary dramatically, for example, according to thetype of semiconductor wafer materials used and the type of doping used.Thus, they can be expected to be different for metals, n-typesemiconductors, p-type semiconductors and combinations thereof. Forexample, electrochemical reduction of metal ions from solution for metalelectrodeposition on the semiconductor wafer can be achieved either viathe conduction band (electron capture process) or the valence band (holeinjection process) for n-type semiconductor wafers, whereaselectroreduction is only possible via a hole-injection process at p-typesemiconductor wafers (in the dark), or when driven into inversion. Inaddition, the semiconductor material (including its band-gap and energyof band edges) and the dopant concentration (including its flat bandpotential and depletion layer thickness) can determine theelectrochemical characteristics of thesemiconductor/insulator/electrolyte (SIE) contact.

In order to allow cathodic conduction band processes at 125 mm orlarger, p-type semiconductor wafers and anodic valence-band processes at125 mm or larger, n-type semiconductor wafers, photon excitation ofvalence-band electrons over the band gap is necessary. This can beachieved by illumination of the semiconductor wafer, for example, viaillumination through the electrolyte solution or from the back-side ofthe semiconductor wafer. Selectivity can be obtained in several ways.For example, careful selection of the light wavelength will activateelectrochemical processes only at those semiconductor wafers or oxideswhere either the complete band gap can be crossed or gap states can beactivated to mediate the electrode reaction. Alternatively, a narrowlaser beam can be used to directly write an etched or deposited pattern,or a mask can be used to illuminate only certain regions of thesemiconductor wafer surface.

In one embodiment, the electrochemical process involves theelectrodeposition of a metal layer on a 125 mm or larger semiconductorwafer. In such a process, the semiconductor wafer acts as the negativeelectrode (cathode) and provides the electrons required for theelectrodeposition of the metal. The electrodeposition process alsoincludes providing a light source in order to facilitate theelectrodeposition of the metal layer on semiconductor wafers with low orno electrons such as p-type silicon.

In another embodiment, the electrochemical process involves theelectroetching and/or anodization of a metal layer from a 125 mm orlarger semiconductor wafer. In this case, the electrochemical processrequires positive charges and the semiconductor wafer acts as thepositive electrode (anode). Hence, in the case of n-type silicon, theelectrochemical process also includes providing a light source in orderto facilitate the electroetching and/or anodization of a metal layerfrom the semiconductor wafer. The electroetch or anodizing process willinclude a metal layer comprising one or more metals selected from Al,Ti, Zr, Nb, Hf, Ta, W, Mo and Cd. The semiconductor wafer can compriseSi, Ge, In, Ga, Sb, P and any combination thereof.

In this regard, FIG. 3 depicts the current-voltage characteristics(scanning towards negative voltage) for n-type and p-type Si/SiO₂/HfO₂semiconductor wafers in a nickel sulfate bath (0.1M NiSO₄+0.1M H₃BO₃) inthe dark and under white-light illumination (21V, 150 W halogen lamp)during a potentiodynamic scan towards negative potentials (forwardscan). In FIG. 3, the current density i is given in milliamps per squarecentimeter (mA/cm²) and the electrode potential U is given in Voltsversus the Normal Hydrogen Electrode (NHE). The scan rate was 50millivolts per second and the electrode rotation rate was 250 rpm.

As shown in FIG. 3, an n-type semiconductor wafer shows an exponentialincrease of the current at negative voltages past −2V in the dark andunder illumination. The p-type semiconductor wafer does not show anycurrent flow in the dark, and shows a cathodic current for Ni²⁺reduction below −1.5V only if the sample is illuminated with light. Thisphenomenon allows for the selective plating of n-type and p-type regionssimultaneously exposed through mask openings. For example, n-typeregions can be selectively metallized by electrodeposition in the darkand the p-type regions can be metallized with another metal of choice byphoto-electrodeposition. In the latter case, both the n- and p-typeareas are plated (i.e. the metal already deposited on the n-type areasgets another metal coating on top), or by the correct choice ofdeposition potential, the p-type regions are metallized selectively (noadditional plating in n-type regions).

For p-type semiconductor wafers, the current becomes limited by thelight intensity at sufficiently negative applied potentials. Theincident photon flux and thus the measured photo-current are lowered iflight is absorbed by the solution and by the deposited metal. Thecurrent density for plating at p-type semiconductor wafers can becontrolled by the light-intensity. For example, pulse plating can bedone at constant potential by strobing or chopping the light beam. Thecurrent-voltage characteristics show the selectivity of metal depositionon n-type and p-type semiconductor wafers. According to the above givenexample, Ni could be deposited selectively in the dark on n-type regionsat potentials more negative than −2V (by applying constant voltage orconstant current). After the metal has been deposited in the n-typeregions, Ni could be deposited selectively at the p-type regions underillumination at potentials between −0.9V and −1.8V.

On the other hand, if the current-voltage characteristics are obtainedin the positive potential ranges, n-Si would require light for obtainingelectrochemical currents and p-type would not need light for theelectrochemical reactions. Hence, for electroetching/anodizationreactions, light would be required for n-type semiconductor wafers.

The electrodeposition of select metals on resistive substrates accordingto the invention and the processing conditions used are discussed inU.S. patent application Ser. No. 11/050,790 filed Jan. 27, 2005 andassigned to International Business Machines, the entire disclosure ofwhich is incorporated herein by reference.

FIG. 4 depicts an arrangement as described for FIG. 2A, but whereselective photo-electrodeposition of a metal pattern 9 on a blanket gatedielectric 2 is achieved by illumination of the semiconductor wafer witha light source 20 through several openings in a mask 13 while applying acurrent to the semiconductor wafer 4 with an electrical contact 5 andthe counter electrode 6. FIG. 4A depicts an arrangement forphoto-electrodeposition and FIG. 4B shows the patterned metal obtainedin the illuminated regions which where not blocked by the mask. Inaddition, any method of patterning that provides open areas can be usedin order to obtain the desired reaction in the open regions. Forexample, the patterning can be obtained with the help of a photoresiston the wafer.

The electrochemical process can be used in conjunction with bothmetallic and doped or undoped semiconductor wafers of 125 mm or larger.Exemplary doped or undoped semiconductor wafers can be selected from aSi semiconductor wafer, a Ge semiconductor wafer or a (Si—Ge)semiconductor wafer, or a doped or undoped binary, tertiary andquaternary semiconductor wafer comprising Ga, As, P, Sb, In, Se and Al.Other exemplary semiconductor wafers include a doped or undoped II-VIsemiconductor wafer comprising Cd, Zn, Te, Se, S and combination of eachthereof, and a doped or undoped oxide semiconductor wafer comprising Tior Zr oxides, a Cu or Sr based semiconductor wafer or asemiconductor-on-insulator semiconductor wafer selected fromsilicon-on-insulator or silicon germanium-on-insulator combinations.Still other exemplary semiconductor wafers can compriseelectroluminescent polymer selected from polyacetylene, poly(dialkoxyp-phenylene-vinylene, poly(dialkylfluorene) and the derivatives of eachthereof.

As stated, the electrochemical process of the invention includeselectrodeposition processes in which one or more metals selected fromthe group consisting of Ru, Re, Ni, Pd, Co, Pt, Rh, Cr and Mn and anycombination of each metal thereof is deposited on the semiconductorwafer. Other select metals and non-metals selected from the groupconsisting of Os, Ir, Sb, Bi, Sn, In, Ga, Ge, As, Fe, Zn, Cd, Se, Te,Cu, Ag, Au, W, Hg, Tl, Po, Pb, Mo, V, B, C, P, S and any combination ofeach metal thereof can also be deposited on the semiconductor wafer.

FIG. 5 depicts an electrochemical apparatus that can be used in thedescribed electrochemical processes of the invention. The design of theapparatus is aimed towards processing 125 mm or larger, particularly 200mm or 300 mm semiconductor wafers. However, the apparatus can bemodified to handle wafers of any shape or size. The apparatus primarilyconsists of an electrolyte container tank 101. The silicon semiconductorwafer 111 is held by a tool head 102 equipped with pneumatic sealing anda ring seal 103. The ring seal 103 pushes the semiconductor wafer,against the metal plate 104, thereby preventing the liquid from reachingthe back side of the semiconductor wafer. The metal plate 104 provideselectrical contact to the semiconductor wafer. Electrical contact to asemiconductor wafer such as Si can be made by a backside contactarrangement. In addition, electrical contact to the semiconductor wafercan be made through an opening in an oxide layer. A conductive orelectric pathway from the point of contact to the dielectric on thesemiconductor wafer can pass one or more interfaces and provides theelectrical current path for the electrochemical process.

Alternatively, the electrical contact can also include a dry solid-statecontact. A dry solid-state contact to a semiconductor wafer can includean ohmic contact, which is typically created by providing a highly dopedsurface (about 10¹⁹ cm⁻³) through implantation of dopant elements orcreation of surface defects. Further, certain metals can also be appliedto the surface of the semiconductor wafer in order to facilitateelectrical connectivity. For example, metals with low work functionssuch as indium can provide an ohmic contact for n-type semiconductorwafers. Metals with high work functions can provide an ohmic contact top-type semiconductor wafers. The apparatus further consists of a counterelectrode 105. The counter electrode in this configuration is amesh-type electrode so that the semiconductor wafer can be illuminatedthrough the solution. The illumination is provided by a light source107, whose wavelength can be chosen depending on the required energylevels for the desired electrodeposition. The light source can bemonochromatic such as a laser or a composite light source such as ahalogen lamp. Further, the light source can include an arrangement tovary the light intensity in order to control the reaction rates.

The electrochemical apparatus of FIG. 5 is particularly useful if theplating solution is transparent or semi-transparent to the light sourceso that sufficient amounts of light can penetrate to the semiconductorwafer to facilitate the electrochemical reaction. The apparatus can alsoinclude a shutter 106 disposed between the semiconductor wafer and thelight source. The apparatus can be used for pulse and pulse-reversalmodes of electrochemical processing of the semiconductor wafers. Themetal contact 104 for the semiconductor wafer 111 is connected to oneend of a power source 108 so that the semiconductor wafer can act as thecathode or the anode depending on the nature of the electrochemicalprocess being performed. For example, in the case of electrodeposition,the semiconductor wafer, e.g., p-type silicon, is the negative electrode(cathode). Alternatively, in the case of etching or anodizing, thesemiconductor wafer, e.g. n-type silicon, is the positive electrode(anode). The counter electrode is then connected to the opposite end ofthe power source 109 to complete the electrical circuitry for eachelectrochemical process.

FIG. 6 depicts a modification of the tool head of FIG. 5. In thisarrangement, metal contact 204 is a mesh-type metal contact forproviding electrical contact to semiconductor wafer 201, and the lampassembly 207 is placed within the tool head 102. Such design isadvantageous with electrochemical processing conditions in which theelectrolyte is near-opaque or opaque to light. In this case, the lightsource helps in generating the current carriers (electrons or holes)directly from the back of the semiconductor wafer without being absorbedby the electroplating solution. The counter electrode 205 can be a metalsheet or a mesh-type electrode. The apparatus can also include a shutter106 disposed between the semiconductor wafer and the light source 207.

FIG. 7 depicts a tool modification in which uniform electrical contactis provided to the semiconductor wafer with a spring-loaded metal plate310. Such an arrangement can minimize a non-uniform contact between thesemiconductor wafer and the metal plate. The spring loaded metal plate310 is electrically connected to a back plate 304. As the semiconductorwafer 301 pushes against the ring seal 103, the springs provide uniformpressure distribution on the surface of the semiconductor wafer andprovide uniform current distribution across the back of thesemiconductor wafer.

Alternatively, instead of using a spring-loaded metal plate, a spongy ormesh contact 310′ can be used to distribute the current uniformly acrossthe semiconductor wafer. Further, in order to enhance the uniformcurrent distribution, another high-conducting mesh 311 is connected tothe spring-loaded plate 310.

FIG. 8 depicts a further modification of the tool head of FIG. 7. Inthis case, the apparatus combines the modification of FIG. 6. The springloaded plate 310 along with a high-conductivity mesh 311 providesuniform current distribution to the back of the semiconductor wafer 301when it is pushed against the ring-seal 103. The lamp assembly 207 isplaced inside the tool head so as to enable electrochemical processingof semiconductor wafers in which the electrolyte used is translucent oropaque to the light source.

FIG. 9 shows the apparatus modification in which the single counterelectrode 105 and the light source 207 are contained within assembly501. The assembly can be positioned in the tank and used to illuminatethe semiconductor wafer. This arrangement can be used in the case oftransparent or semi-transparent solutions. The glass (or othertransparent material) case 502 housing the lamp assembly 207 (for e.g.,LED or halogen lamp) is protected against electrolyte leaking or seepingwith o-rings 503. The counter electrode 105 in the form of a mesh isheld in place with the help of o-rings 503. The lamp assembly 207 can bedesigned for any number of lamps and orientation. Two such lamp designsare shown in FIGS. 9A and 9B, in which low-intensity lamps 507 andhigh-intensity lamps 508, respectively, can be arranged for illuminatingthe semiconductor wafer.

EXAMPLES

Copper Electrodeposition:

A plating solution comprising from 1 g/liter to 300 g/liter of CuSO₄, 1ml/liter to about 250 ml/liter of H₂SO₄ and 1 to 10000 ppm of Cl⁻ can beused. For example, the plating solution can comprise about 240 g/literof CuSO₄ and about 100 g/liter of H₂SO₄, having a pH from about 1 toabout 2. The source of the Cl⁻ is sodium chloride. In addition, otherinorganic constituents such as bromides, iodides, fluorides, sulfides,sulfates, boric acid, borates and metal salts & organic additives suchas surfactants, brighteners, accelerators, suppressors and levelers canbe added.

In electroplating processes using the above plating baths, one or moreof several methods of applying a current or voltage can be used. Theseinclude, for example: application of a constant current from 1 mA/cm² to50 mA/cm² or equivalent potentials (electrode potentials of −2V to −3Vversus NHE); and pulse plating with a first current from 5 mA/cm² to 250mA/cm² for about 20 milliseconds to about 5 seconds such as about 0.1second, and a second current from 1.0 μA/cm² up to 2 mA/cm² for about0.1 seconds to about 10 seconds, including pulse plating with potentialsof −2V to 3.5V versus NHE for about 1 cycle up to about 500 cycles suchas 25 cycles. The temperature during processing can, for example, rangefrom 20° C. to 90° C.

Included in the above processing conditions are those in which there isapplied a constant current of about 10 mA/cm² for about 30 minutes atroom temperature with agitation at about 100 rpm.

FIG. 10 shows an example of a 200 mm semiconductor wafer electroplatedselectively with copper using the above mentioned bath and operatingconditions. Copper was electroplated into deep vias with aspect ratiosgreater than 10, i.e, vias ranging from 1 to 40 μm in height and 0.1 to2 μm in width. The semiconductor wafer used in this example isn-Si/TaN/Ta/Cu. The TaN/Ta/Cu layers were deposited using physical vapordeposition. The layers were very thin in the order of 100-300 Å. Theliner material, typically Ta/TaN, and seed, typically Cu or Ru, wasremoved from the top of the vias using Chemical Mechanical Planarization(CMP) method prior to plating. The CMP process leaves the liner/seedlayers only in the via regions making it the preferential conductivepath. This arrangement forces the current to be conducted only in thevia regions and hence Cu plates selectively.

Rhenium Electrodeposition:

A plating solution comprising from 1 g/liter to 100 g/liter of NH₄ReO₄and about 1 ml/liter to about 250 ml/liter of HCl (38%) can be used. Forexample, the plating solution can comprise about 10 g/liter of NH₄ReO₄and about 10 ml/liter of HCl (38 wt. %), having a pH from about 1 toabout 2. In addition to NH₄ReO₄, other perrhenate salts and inorganic Resalts can be used. In addition to HCl, other chloride salts can be used.In addition, other inorganic constituents (such as bromides, iodides,fluorides, sulfides, sulfates, boric acid, borates and metal salts) andorganic additives (such as surfactants), can be added.

Patterned MOS structures were prepared by the electrodeposition ofrhenium (Re) with p-type semiconductor wafers using a thick SiO₂ maskwith openings from 1 μm×1 μm to 400 μm×400 μm. The Re was depositedselectively on top of a high-k/SiO₂/Si stack. The high-k material wasHfO₂ and HfSiO, 3 nm and 4 nm, respectively, which was prepared byMOCVD. SiON (1 nm) was prepared by rapid thermal oxidation and the SiO₂(1 nm) was a chemical oxide. FIG. 11 is a graphical representation ofcapacitance-voltage and current-voltage characteristics for Re gatesmeasured with a 100 μm×100 μm MOS test structure. The Re gates wereprepared on 200 mm, p-type Si semiconductor wafers. The figure shows theuniformity of the electrical characteristics across the wafer. The Rewas deposited potentiostatically under white light illumination (−3V vs.SCE; 120V/500 W halogen lamp, 100 rpm).

In electroplating processes using the above plating baths, one or moreof several methods of applying a current or voltage can be used. Theseinclude, for example: application of a constant current from 3 mA/cm² to50 mA/cm² or equivalent potentials (electrode potentials of −2V to −3Vversus NHE); and pulse plating with a first current from 5 mA/cm² to 250mA/cm² for about 20 milliseconds to about 5 seconds such as about 0.1second, and a second current from 1.0 μA/cm² up to 2 mA/cm² for about0.1 seconds to about 10 seconds, including pulse plating with potentialsof −2V to 3.5V versus NHE for about 1 cycle up to about 500 cycles suchas 25 cycles. The temperature during processing can, for example, rangefrom 20° C. to 90° C.

Included within the above processing conditions are those in which thereis applied a constant current of about 10 mA/cm² for about 120 secondsat room temperature, with agitation at about 400 rpm.

FIGS. 12 ad 13 show XRD characteristics of the metal layers obtained byelectroplating as compared to other conventional techniques such asevaporation, chemical vapor deposition and sputtering. Ru and Re weredeposited by the conventional techniques under standard conditions. Asshown in FIGS. 12 and 13, the crystal structure orientation(100/002/101) for both ruthenium and rhenium vary depending upon thedeposition process used. In the case of ruthenium (FIG. 12), the CVD andPVD/annealed exhibit quite similar crystal structure orientation in thatthe 002 intensity dominates the XRD and there appears to be very littlecontribution of 100 (comparing the peak intensities of both 002 and101). In comparison, the ruthenium that is photo-electrodeposited by theprocess of the invention exhibits a crystal structure orientation inwhich 101 dominates the XRD and 100 and 002 exhibit similar intensities.

In the case of rhenium (see, FIG. 13), the as deposited evaporated Re(spectrum b) and the PVD/annealed Re (spectrum e) exhibit quite similarcrystal structure orientation in that all three crystal orientationsexhibit similar intensities in the XRD. In comparison, the Re that isphoto-electrodeposited by the process of the invention exhibits acrystal structure orientation in which 002 peak dominates and there isvery little contribution from 100.

1. An anodic electrochemical process of a 125 mm or larger, n-typesemiconductor wafer with a metal layer, the process comprising:positioning the 125 mm or larger, n-type semiconductor wafer in anelectrolytic solution; positioning a counter electrode in theelectrolytic solution; illuminating a front side or the back side of then-type semiconductor wafer with a light source; and applying an electriccurrent to the semiconductor wafer and to the counter electrode.
 2. Theprocess of claim 1 wherein the anodic electrochemical process is anelectroetching process of the metal layer or an anodization process ofthe metal layer disposed on the semiconductor wafer.
 3. The process ofclaim 1 wherein the electrochemical process is an electroetch oranodizing process, and the semiconductor wafer comprises one or moremetals selected from Al, Ti, Zr, Nb, Hf, Ta, W, Mo and Cd, or thesemiconductor wafer is a semiconductor wafer comprising Si, Ge, In, Ga,Sb, P and any combination thereof.
 4. The process of claim 3 wherein theelectric current is applied as a constant current, constant potential, apulse current or a pulse potential.
 5. An apparatus comprising: a tankfor holding an electrolytic solution; a conducting surface in contactwith a surface of a semiconductor wafer, said conducting surface inelectrical contact with an electric power source; a light source facingan opposite surface of the semiconductor wafer; and an electrode inelectrical contact with the electric power source, wherein the electrodeis positioned in the tank so that the electrode can come in contact withthe electrolytic solution.